In a preferred, although not exclusive, application, the output shaft of the rotary bench carries, integrally in rotation, an aerodynamic surface of an aircraft, such as a control surface of a missile or another device circulating at high speed in a fluidic medium, and it is then subjected to evolutive and high stresses (radial loads) and hinge moments (torques), generated by the aerodynamic forces applied on the control surface according to the deflection angle of the latter.
Thus, the aim of the dynamic load bench of the present method, system and device is to reproduce both radial loads as well as variable torques, depending on the rotation angle adopted by the output shaft of the rotary bench, being representative of the deflection carried out by the control surface. And the value of these stresses and moments will be able to be modulated as a function of time so as to represent the different flight points of the missile (slow and/or quick variations of the speed, trajectory and altitude changes, . . . ) and come as close as possible to the actual conditions being met, that is, aerodynamic operational loads undergone by the actuator so as to, subsequently, optimize the design thereof.
Dynamic load benches for such actuators are already known, being based on controlled reproduction means of the torque only, from a torsional rod or from a torque generator.
In the first case, the torsional rod of the bench reproducing means is linked, on the one hand, directly to the shaft of the rotary bench to be tested and, on the other hand, is restrained so that, when the actuator angularly clears, it generates a torque being proportional to the rotation angle of the deflection. Although having a very basic design, such torsional rod means apply return torques that do not allow to generate destabilizing and/or evolutive loads as a function of the deflection of the control surface. Furthermore, they are too limited and do not allow to validate reliably the performance of the actuators in actual flight conditions, so that, through a lack of clear and accurate data, the torsional rod reproduction means are over-specified so as to keep margins.
In the second case, the torque generator of the reproduction means is directly coupled to the actuator and is defined, as a result of required dynamic performance, by a hydraulic torque motor. If high torques can be thereby tested, on the other hand, the relative movements occurring between the torque motor and the actuator generate problems as a result of their inertia and their rigid link as, when the shaft of one of them rotates, the other tends to counteract, so that shocks could occur up to the destruction of the equipment. This could be amplified by the hydraulic engines being significantly powerful.
In addition to only applying the torque on the rotary shaft to be tested (another specific bench being required for radial loads), these dynamic load benches do not often meet all the desired expectations and requirements such as:                having a lower apparent inertia and a nil coupling play so as not to disturb the actuator to be tested; ideally, behave on a dynamic standpoint, as a mere torque;        having available a high pass band of the torque slaving loop, at least of double that of the actuator to be tested so as to reproduce the instructed torque profile, without any significant delay;        having available a well higher speed and acceleration saturation relative to that of the actuator;        tolerating functional misalignments between the actuator and the bench for an easy implementation, involving some flexibility of the link often incompatible with a high pass band of the torque loop;        ensuring an efficient management of the applied torques so as to avoid any overload, overspeed and accidental abutment, that could prove to be damaging, and this even in the case when the actuator should become defective (supply being cut off, breakdown, etc.).        
Of course, from U.S. Pat. No. 7,080,565, a dynamic load bench is also known enabling to apply on the rotary shaft of the actuator to be tested radial stresses and dynamic torques. However, the controlled means for reproducing them also comprise too this end two distinct equipment independently the one from the other with specific sub-assemblies. It is in particular necessary to mechanically decouple the application of radial stresses and torques by means of sophisticated Cardan joint, slide, or jointed coupling systems. Furthermore, an encoder should be provided for measuring the rotation of the output shaft of the actuator. And the numerous present sub-assemblies and equipment furthermore limit the excitation of the bench at high frequencies able to generate prejudicial interference resonances and also result in a tricky implementation.
From patent EP 0,239,264, a trial apparatus is further known for applying a mere torque on co-linear input and output shafts of a transmission type gear box for an aircraft engine. To this end, it comprises more specifically a device for applying the torque to two parallel and symmetric modules relative to the shafts, and comprising multiple gear devices driven by rotary actuators so as to be able to reach the high power of the engine.